1. Field of Invention
This invention relates to an erasable magneto-optic media recording system which provides a magnetic biasing flux at a point of optical incidence on the media and, more particularly, to such a system which provides such magnetic biasing flux without interfering with the path required for the travel of the media.
2. Description of the Prior Art
Magneto-optic media is known which has information recorded thereon or read therefrom by means of a focussed spot of light utilized in conjunction with a directed magnetic bias. In one such form the media is magneto-optic tape which is recorded upon or read from by means of a helical scanning optical head in known fashion. In such a system, when recording or erasing, a light beam is focussed, by suitable beam forming means, onto successive spots on the tape to soften the tape which then, by means of a magnetic bias of one polarity or another, deforms the surface layer of the tape in a desired fashion to effect the process of recording or erasing data. The change in the surface optical reflectance characteristics is typically recognized by a differential detection scheme using the Kerr effect and thus is used to read the data.
A problem arises in providing the desired magnetic bias at the point of incidence of the light beam on the tape in that a magnetic bias is required at all locations of the scan of the tape by the beam and the relative velocities of the scanner and tape are different. This means that either a scanning field must follow the optical scan or the magnetic field must be simultaneously present at all locations. Supplying a biasing field solely from the optics side of the tape is unpractical because of interference with electro-optical elements of the beam forming means and excessive power is required for providing the field over a long air gap.
A device on the side of the tape opposite that being recorded upon and which rotates with the scanning optical head will interfere with the path that the tape requires for feeding and exiting the scanner wheel of the scanning optical head.